The present invention relates to sheet-feed type scanners, and more particularly to such a sheet-feed type scanner which uses a document sheathe to hold document so that document will not be jammed or damaged when scanning.
In a regular sheet-feed type scanner, the image sensor is immovable, and document is moved by a transmission mechanism over the image sensor. This structure of scanner needs less table space, however it still has numerous drawbacks as outlined hereinafter.
1. Document tends to be damaged. When a document, for example, a picture, is moved over the rollers of the transmission mechanism, its surface tends to be damaged. PA1 2. Document tends to be jammed. Because document touches the rollers of the transmission mechanism during scanning, it tends to be jammed when it is obliquely inserted into the document feed hole. PA1 3. The troubleshooting and maintenance works are complicated. Because the size of this type of scanner is small and its internal mechanical mechanism is complicated, it is difficult to eliminate the trouble when document is jammed. PA1 4. The scanning quality is low. Because document touches the rollers of the driving mechanism, document tends to be stained or rubbed, causing a shadow or black lines to occur in the scanned image. PA1 5. The application range is limited. This structure of scanner is not practical for scanning document of irregular edges or thin document because they tend to deviate from the course during scanning.